Energy Recovery Ventilator with Heat and Membrane Humidity Exchangers for Commercial Application
Commercial Ventilation: Heat and Humidity Recovery vs. No Energy Recovery
An air-to-air heat exchanger that transfers both sensible and latent heat between the exhaust air stream and the fresh air stream using one of a number of membrane-based technologies.
Item ID: 461
Technical Advisory Group: 2010 HVAC TAG (#3)
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 2.58 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- This is required by code in several applications, the PNW doesn't need the additional cost for humidity exchange and if the heat is gas, the savings will be gas.
- Would be interesting to hear about, although a longshot for our climate.
- For both residential and commercial applications, we need to get more analytical. With the relatively mild climates of the NW, do the fan power requirements eat up the energy savings, unless we pay for bypasses around the ERV? What buildings actually need enthalpy control, instead of just sensible heat, and in what climate zone?
- I am unsure about this technology in retrofits.
- Unless you have a high demand for dehumidification, this technology is seldom cost-effective.
Energy recovery ventilators (ERVs) are similar to heat recovery ventilators (HRVs) (ET #20 Heat Recovery Ventilator for Commercial Application) in that they transfer sensible heat energy from outgoing exhaust air to incoming outdoor air. Unlike HRVs, ERVs also transfer the latent energy of the moisture in the air. The ERV recaptures cooling and heating energy while controlling humidity extremes without mixing the two air streams. The key to this innovation is polymer membranes that are moisture-permeable, allowing humidity to be exchanged between the indoor and outdoor airstreams.
In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air through membrane exchange without allowing odors or pollutants in. In hot and humid climates, ERVs help to maintain (but do not reduce) the interior relative humidity (RH) in the process of cooling outside ventilation air. Reducing the RH in the summer decreases the mechanical cooling required, which makes this technology particularly suitable in hot and humid or very cold climates. A small handful of companies (e.g., Building Performance Inc. and dPoint) offer this technology using a microbe- and mold-resistant polymer (e.g., polypropylene) membrane that requires no moving parts (other than the HVAC fans external to the ERV).
Preconditioning the supply air can reduce energy consumption for heating and cooling. A study by the National Research Council of Canada showed that the ERV saved an additional 20% of dehumidifying energy and reduced cooling costs by 12%. The U.S. DOE Building Technologies Program states that enthalpy/energy recovery devices can save 65% of the energy consumed to condition outside air.
Baseline Description: Conventional HVAC without heat recovery
Baseline Energy Use: 10.5 kWh per year per square foot
The 2009 Commercial Building Stock Assessment (CBSA) gives the actual electrical building Energy Use Index (EUI) for various types of heating and cooling systems (CBSA Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year, indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. (For all commercial buildings, the corresponding values are 19.9 and 9.4 kWh/sf/year, respectively, for a heating and cooling use of 10.5 kWh/sf/year.)
Because this technology can be applied to many types of commercial buildings, a baseline heating and cooling energy use of 10.5 kWh/sf/year is assumed (NEEA, 2009).
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 65%
Low and High Energy Savings: 12% to 70%
Energy Savings Reliability: 3 - Limited Assessment
Energy savings depend on climate type and the baseline system operation. The USDOE Federal Energy Management Program (FEMP) states that ERV systems have been shown to reduce HVAC energy consumption by up to 70% (FEMP Promising Technologies List). Other USDOE documents state that this technology can reduce outside air conditioning (heating and cooling) energy costs by 65% (Roth, et. al., 2002).
Energy Use of Emerging Technology:
3.7 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This technology could be used for virtually any commercial building with electric space heat and without an existing economizer. The total square footage of the entire commercial building stock in the Northwest that has conditioned space that is electrically heated could be used for this application (84.7% x 27.1%, from Table C-GB13). The total commercial floor space that would benefit from a retrofit with this technology is, thus, estimated as the conditioned space or 2,640,946,000 sf x 27.1% = 715,696,366 sf. This is the same as the square footage that is appropriate for retrofit with a heat recovery ventilator (ET #20 Heat Recovery Ventilator for Commercial Application).
Regional Technical Potential:
| || Total Commercial Floor space || % Conditioned || Conditioned space |
| Source, units || (NEEA, 2014) (sf) || (NEEA, 2009, App C ) || (sf) |
| || 3,118,000,000 || 84.7% || 2,640,946,000 |
4.88 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
Emerging Technology Unit Cost (Equipment Only): $0.75
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.20
Baseline Technology Unit Cost (Equipment Only): $0.01
Total installed costs,including overhead and profit, are estimated to range from $1.50 to $8.40/cfmfor heat wheel recovery units rated for 25,000 cfm down to 1,000 cfm (RS Means,2015 Facilities Construction Cost Data). Under peak conditions, one ton ofcooling requires about 170 cfm (Roth, et. al., 2002). One ton also serves about400 sf, so installed costs are approximately $2.25/cfm (for a 6,000 cfm ratedunit) x 170 cfm/ton x ton/400 sf = $0.95/sf.
Simple payback, new construction (years): 1.2
Simple payback, retrofit (years): 1.5
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.